The present invention relates to combustion engines and more particularly relates to an improved piston and ring design for combustion engine which piston may be used in connection with both gas and diesel fueled engines.
Basically, a piston for a combustion engine consists of a generally cylindrical body enclosed at the top by a piston head connected to the crankshaft of an engine by a connecting rod. Power is generated as the fuel/air mixture combusts causing the piston to reciprocate. A transversely extending boss within the cylinder body defines a journal which receives the wrist pin connected to the connecting rod. Annular grooves separated by lands to piston heads receive rings. Two types of rings are received in the grooves: (1) compression rings; and (2) oil rings. Compression rings prevent combustion gases from leaking past the piston into the crank case below the piston. The compression rings also wipe some of the oil from the cylinder wall when the piston is on the downward stroke. Compression pressure behind the compression rings force the compression rings against the cylinder wall.
Good lubrication requires an oil film to be distributed between the piston and cylinder wall. The purpose of oil rings is to control the distribution of oil and prevent the oil from escaping to the combustion chamber. The conventional oil ring defines a plurality of small holes or slots spaced around the groove. The oil control ring scrapes oil from the cylinder and directs it through these holes. There are variations to this conventional design which can be found in the prior art. Representative piston designs are as follows:
The early patent to King, et al, U.S. Pat. No. 1,519,918, shows a piston having annular ring receiving grooves which are downwardly and outwardly beveled to enhance lubrication.
U.S. Pat. No. 2,560,253, shows a piston having an oil ring which is spring-loaded.
Corrugations and notches in the spring and slots provide passageways through which oil scraped from the cylinder walls by the ring may flow to the interior of the piston.
In U.S. Pat. No. 2,860,614, a piston is shown in which lubricant escapes from the underside of the piston and passes through passages in the skirt. A channel may be provided at the base of the cylinder to collect lubricant as it runs down the cylinder walls and as it leaves the passages in the skirt.
In U.S. Pat. No. 2,187,724, shows a piston and ring assembly having oil ring grooves spaced downwardly from the compression ring grooves and a gas pressure groove between the compression grooves and the oil ring groove. The gas-pressured groove receives the gases that manage to blow by the compression rings.
In U.S. Pat. No. 2,857,218, shows a piston having two oil scraper rings that are inserted in the proximity of the lower end of the piston.
In U.S. Pat. No. 4,462,601, shows a piston having a duct provided between the high pressure of the seal and the bottom of the piston ring groove. The resistence against gas flow between the high pressure side and the piston ring along the piston and cylinder walls is greater. Thus, the piston ring will be forced into a sealing position when the engine is pressurized.
In U.S. Pat. No. 4,836,093, shows a piston having at least one aperture in at least one compression ring groove. The aperture is in fluid communication with the interior of the hollow skirt portion of the piston communicating lubricant gathered in the compression ring groove into the interior of the hollow skirt so that the lubricant can return to the crank case.
Thus, from the foregoing, it can be seen that the various arrangements for removing, collecting and redistributing the lubricant or oil film occurring on the cylinder walls. However, many of these arrangements are expensive, difficult to manufacture requiring extensive machining operations, or are ineffective to achieve enhanced lubrication.
Briefly, the present invention provides an improved piston for a combustion engine. The piston has an oil trap feature which improves lubrication and cooling. The piston is generally cylindrical having a body having a head and a depending skirt. The piston head may be integrally formed as part of the body or may be inserted in top of the piston head and maintained by a press fit. The inside of the head is shaped to force lubricating oil to interior oil traps formed within the piston head. The exterior of the piston defines one or more annular grooves, which receive a compression ring. At least one oil ring extends annularly about the exterior of the piston. An oil trap extends within the interior cavity of the piston head located interiorly of the oil rings. The oil trap has a bottom surface which extends about the interior wall of the piston and which extends upwardly forming an acute angle with the interior piston wall. A plurality of holes extend through the piston wall communicating with the oil trap. The oil trap captures lubricant on the downward stroke of the piston in the cylinder and delivers the lubricant through the holes on the upward stroke. This pumping of fluid on the upward stroke will also provide a cooling effect as the oil moving between the piston and cylinder will absorb heat and scrape or wipe dirt off the cylinder walls and piston keeping the surfaces clean.
In a further aspect of the present invention, an improved oil ring assembly is received in the annular oil grooves. The oil ring assembly includes an upper oil ring which will wipe oil off the cylinder walls as the piston reciprocates. An expander ring is interposed between the upper oil ring and the lower oil ring. The expander ring has a generally wave-like configuration with holes extending through the ring. The lower ring is generally flat having a plurality of notches or grooves extending around the periphery of the lower ring. The small notches allow the oil to move downwardly as the piston moves upwardly. The oil ring assembly can be integrally formed or can be separate components inserted and assembled within the oil grooves.
In addition, the piston assembly includes a bridge member extending between the interior bosses which define the journal bearing surfaces which receive the wrist pin at the upper end of the piston rod. The bridge member extends upwardly to provide a support for the piston head engaging the interior or underside of the piston head.
The present invention also provides a single ring assembly which includes at least one compression ring and an oil trap and pumping feature.